1. Field of the Invention
The present invention relates to the decomposition of a polysiloxane to a silicon compound having a lower molecular weight.
Further, the present invention relates to a method for producing an alkoxysilane which is one of important intermediates used in a silicone industry.
2. Description of the Related Art
Since a polysiloxane is a chemically stable compound, it should be treated at high temperature optionally in the presence of an alkali or an acid to decompose it.
A synthesis reaction of an alkoxysilane compound using a decomposition reaction of a polysiloxane is known, but a yield is low. That is, Japanese Patent KOKAI Publication No. 132590/1989 discloses a process for producing an alkoxysilane of the formula: EQU R.sup.3.sub.b SiH.sub.c (OR.sup.2).sub.4-(b+c)
wherein R.sup.2 is an alkyl group, R.sup.3 is a substituted or unsubstituted monovalent hydrocarbon group, b is 1, 2 or 3, and c is 0, 1 or 2 comprising reacting an alkoxysilane of the formula: EQU R.sup.1.sub.a Si(OR.sup.2).sub.4-a
wherein R.sup.2 is the same as defined above, R.sup.1 is a substituted or unsubstituted monovalent hydrocarbon group, and a is 0, 1, 2 or 3 with a polysiloxane in the presence of a titanium compound catalyst.
According to this process, for example, tetramethoxysilane and a polymethylhydrogensiloxane of the formula: EQU Me.sub.3 SiO--(MeHSiO).sub.40 --SiOMe.sub.3
are reacted to obtain dimethoxymethylsilane. Further, tetraethoxysilane and octamethylcyclotetrasiloxane of the formula: EQU (Me.sub.2 SiO).sub.4
are reacted to obtain diethoxydimethylsilane.
It is assumed that, in this process, the desired alkoxysilane would be synthesized through cleavage of a Si--O bond of the polysiloxane by the titanium compound used as the catalyst and an insertion reaction of the alkoxy group from the raw material alkoxysilane between the cleaved bond (depolymerization reaction).
While this process has advantages that hydrogen chloride or chlorosilane is not by-produced because it is a halogen-free reaction, it has disadvantages that a yield of the desired product is decreased because of many side reactions, the process requires a troublesome fractionating step, and a large amount of by-produced polysiloxane remains as a residue.